Hybrid vehicles generally consist of an electric traction motor, or motors, that drive the vehicle wheels, storage batteries to supply electrical energy to the traction motor, and some sort of generator/alternator driven by an internal combustion engine (ICE) to charge the batteries and/or provide the power for the traction motor. In a series hybrid vehicle there is no mechanical connection between the drivewheels and the ICE. The ICE is used only to drive the alternator/generator. The engine/alternator combination provides a means of converting the chemical energy of the fuel to electrical energy.
This particular invention is directed specifically to a series hybrid type of vehicle. The series hybrid design described has several advantages:
(1) If the batteries are of appropriate storage capacity, the engine/alternator combination, more commonly known as an auxiliary power unit (APU) or range extender, will not be turned on for slow speed, short trip usage. Therefore, during this type of operation, the vehicle emits no exhaust emissions. The owner charges the batteries at home, and uses the vehicle as a "grocery getter." A significant portion of its usage will be emission-free.
(2) The APU would come into usage only when the vehicle has depleted its stored electrical energy, either by driving long distances and/or operating at high power levels at freeway speeds. Onboard microprocessors and controllers monitor such conditions and would be able to anticipate the start-up of the APU. With such anticipation, the APU can be started under very controlled conditions to minimize exhaust emissions, the vast majority of which are generated at start-up.
The design of a series hybrid vehicle places heavy emphasis in utilizing the stored electrical energy (battery) before the chemical (fuel) energy is used by the APU. As such, the traction motor will have been in use for a significant period of time prior to the need for the APU. Due to inherent energy conversion losses in electric traction motors, generators, and internal combustion engines, each of these systems requires a cooling system. The purpose of the cooling system proposed by this invention is to scavenge waste heat normally dissipated from the electric traction motor and utilize it to elevate the coolant temperature of the (ICE) prior to start-up, to thereby reduce the output of emissions. More particularly, the cooling of the traction motor can be done in such a way that the resultant waste heat energy becomes available for a system that could use it; i.e., the ICE.
In a hybrid vehicle, start-up of the ICE is independent from the initial drive-away of the vehicle since the ICE is not provided for powering the wheels of the vehicle. When this is possible, the conditions under which engine start-up occurs can be optimized. It is well documented that nearly 80% of a conventional ICE powered automobile's emissions are generated during cold start-up and drive-away, as mentioned above. An engine maintained at some elevated temperature, optimally 125.degree. F. to 180.degree. F., for example, could be started without the need for fuel enrichment, i.e., air/fuel ratios richer than stoichiometric (chemically correct A/F ratio), resulting in significantly improved exhaust emissions. The invention, therefore, provides a cooling system in which the ICE is preheated by the absorption of waste heat from the traction motor to thereby minimize exhaust emissions.
The cooling system of the invention provides two paths of circulation for the ICE coolant as a function of the temperature of the ICE coolant, both being through the engine, one, however, being through the engine and a first heat exchanger in heat exchanging relationship with the waste heat of the traction motor when the ICE is not running; the other being through a second heat exchanger, such as a conventional radiator, when the engine is running.